The present invention relates to apparatus and procedures for medically responding to an abnormal cardiac event in a subject. In particular, the present invention relates to the emergency medical care of a subject or victim of cardiac arrest.
Cardiac arrest is an event in which a subject's heart abruptly or suddenly stops. The accompanying symptoms and often-unnoticed precursors of cardiac arrest include various heart arrhythmias (e.g., ventricular tachycardia or fibrillation, asystolia, and Pulseless Electrical Activity (PEA)). Other causes of cardiac arrest may include atherosclerotic heart disease, profound anaphylactic shock, major changes in the blood's electrolyte composition, or drug overdose.
Unattended cardiac arrest is generally fatal within a few minutes. However, prompt medical attention can have positive outcomes. If circulation of oxygenated blood through the body is re-established within a few minutes of cardiac arrest, then irreversible ischemic (lack of oxygen) damage to body tissue may be minimized or avoided.
In the common or traditional cardiopulmonary resuscitation (CPR) treatments, the victim or subject's heart is externally massaged or stimulated in order to recirculate blood through the subject's body. The subject is ventilated to provide airflow through the lungs for blood oxygenation. Further, a defibrillator, which sends a strong electric current through the heart, may be used to eliminate the arrhythmic impulses.
Traditionally, medically trained persons or resuscitators are required to administer or deliver CPR. Traditional CPR is delivered manually by alternately compressing the subject's chest by hand in a cyclical fashion, and breathing mouth-to-mouth into the subject's airways. Guidelines published by the European Resuscitation Council and the American Heart Association recommend a chest compression of about 20% of the sternum depth. The adult sternum depth can vary from about 175 mm to 260 mm. Thus, chest compression depths of 35 to 52 mm are recommended. Manually administering chest compressions of these depths can be strenuous and physically demanding, making it difficult to give CPR consistently or properly. Now automated chest compression/decompression devices (CPR devices) are available to mechanically stimulate the heart. These devices compress and decompress a subject's chest in a cyclical fashion. These devices may be incorporated in field portable CPR assemblies or systems (such as the LUCAS™ devices that are sold by assignee Jolife AB of Lund, Sweden).
The automated chest compression/decompression or CPR devices include a pneumatically driven compressor unit, which reciprocally drives a chest contact pad to mechanically compress and/or decompress the subject's chest. The subject is rested in a supine position during CPR administration. The compressor unit is mechanically supported vertically above the subject's chest so that the contact pad is in mechanical contact with the subject's chest about the sternum.
Other useful medical devices (e.g., defibrillators, and pacers) also can be used with the automated CPR devices for additional therapeutic measures. For example, electrical defibrillators may be used to defibrillate the subject's heart separately or in combination with mechanical stimulation of the heart. Barkalow et al. U.S. Pat. No. 4,273,114 describes, for example, an apparatus that may be used for concurrent mechanical chest compression and defibrillation.
Respiratory arrest or otherwise diminished respiratory function often accompanies cardiac arrest. Restoring an adequate supply of oxygen through the subject's airways to oxygenate venous blood is as crucial for the subject's resuscitation as it is to recirculate blood through the subject's body by chest compression/decompressions. In traditional CPR administrations, the resuscitator breathes or blows into the subject's mouth to deliver oxygen into the lungs. Now, ventilation devices or aids are available for use during CPR administrations to improve or time the flow of oxygen to the lungs. Lurie et al. U.S. Pat. No. 6,312,399 B1 describes, for example, an electro stimulator for stimulation of the subject's respiratory muscles during the CPR chest compression/decompressions. The stimulation of respiratory muscles causes the subject to gasp. This gasping increases the magnitude and duration of negative intrathoracic pressure (chest decompression) by which venous blood is drawn to the heart and lungs. The respiratory muscle stimulation may be electronically timed to occur during the mechanical chest decompression phase to match the gasping inspiration of air with the draw of venous blood.
Similarly, Lurie et al. U.S. Pat. No. 5,692,498 discloses use of a pressure check valve to time air flow into a subject's lungs. The pressure check valve is supported in an endotracheal tube, which is installed in the subject's trachea. The valve allows air inflow only when the lung cavity or intrathoracic pressures fall below a threshold pressure, for example, during chest decompression. Accordingly, inflows of oxygenating air during CPR administration can be timed to occur at the same times as when venous blood flow is drawn into the heart by the low intrathoracic pressures.
Consideration is now being given generally to ways of improving or enhancing the efficacy of CPR measures or treatments. Attention is directed to non-invasive techniques and apparatus for oxygenating blood and re-establishing blood flow or circulation in a subject who is a victim of cardiac arrest.